1. Field of the Invention
The present invention relates generally to an apparatus for removing water and gas from oil-based lubricants and the like. More particularly, the invention relates to an improved system for removing entrained, dissolved or emulsified water and other impurities from hydraulic and lubricating oils by means of a circulating system including a heating and vacuum flow loop.
2. Description of the Related Art
A wide variety of industrial, mobile, mining and other applications exist for machine systems wherein a petroleum or synthetic oil is employed as a lubricating or power transmission medium. For example, mechanical power transmission equipment typically includes bearings, gear boxes, chain drives, and the like which require ongoing lubrication. In a typical bearing application, a lubricant, such as petroleum-based lubricating oil is circulated through a bearing housing to flush and lubricate an antifriction bearing. In other applications a lubricant bath is provided, such as for large gear reducers, and lubricant may be circulated from the bath to be cooled and cleaned on an ongoing basis.
Other applications include industrial and mobile oil-based hydraulic systems wherein a natural or synthetic oil is employed both for lubricating purposes and to transmit power. Such systems generally include a positive displacement pump coupled to pressure conduits and valving for transmitting pressurized oil to actuators, such as hydraulic motors and cylinders. Such systems also typically include an oil reservoir having a capacity sufficient to supply anticipated volumetric needs of the system components, as well as to provide sufficient cooling and settling of oil circulated through the components. Additional filtering devices are often included, such as suction strainers upstream of pumps, and high and low pressure filters at appropriate locations in the system to remove dirt, debris and other contaminants.
Due to the lubricating function of the oils employed in applications of the types described above, it is generally important to maintain a relatively low level of solid, aqueous and gaseous contaminants. Such contaminants typically enter systems through seals, such as shaft seals on rotating shafts or linearly extending and retracting cylinder shafts, as well as by the normal internal wear of system components. Certain contaminants, such as water, may enter the oil by condensation, such as along internal walls or baffles of the system reservoir. If left within the system, such contaminants may significantly reduce the usable life of system components, causing accelerated wear of both soft and hard seals, as well as to metal parts. In addition, entrained water and gasses may lead to microscopic level cavitation and subsequent implosion, pitting or otherwise degrading system components. Finally, water and other corrosive materials can often lead to superficial oxidation of metallic parts which further degrades the systems.
Various techniques have been devised and are presently employed for removing contaminants from oil-based lubricant and hydraulic systems. For solid contaminants, conventional filtration is often an effective removal device. Aqueous and gaseous contaminants are, however, often difficult to remove via conventional filtering systems. While filter elements have been devised for capturing and storing water, such elements tend to add significantly to the cost of the systems over time, and may require frequent replacement of filter elements, particularly where water is entrained into or condensed into the system in relatively high volumes.
A different approach to the removal of water and gaseous contaminants from oils is based upon evaporating or flashing such contaminants from the oil by means of heating and circulation of the contaminated oil through a vacuum chamber. A system generally of this type is described in U.S. Pat. No. 2,937,977 issued to Topol on May 24, 1960. As described in that reference, such systems often include an electric heating element over which contaminated oil is circulated to raise the temperature of the oil and any entrained contaminants. The oil is then circulated into a vacuum vessel where emulsified or entrained water is vaporized by a combination of the elevated temperature and the reduced pressure. The dehydrated oil may then be collected and recirculated to the application, while removed water is condensed, collected and disposed of separately.
While dehydrating systems of the type described above represented significant advancements in the treatment of contaminated oils and lubricants, they are not without drawbacks. For example, in conventional systems contaminated oil directly contacts the heating element as it circulates through the system heating unit. Because the systems are designed to raise the temperature of the contaminated fluid to a point required to flash entrained and emulsified contaminants, the heating elements are typically energized and de-energized based upon temperature of the stream of contaminated fluid flowing out of the heating unit. As a result, the heating element is often fully energized to rapidly heat the contaminated fluid, resulting in heating element skin temperatures sufficiently elevated to cause significant degradation of the oil. Moreover, because the incoming flow of contaminated fluid is typically at a substantially lower temperature than the desired temperature for flashing contaminants, the thermal energy required to be input by the heating element is quite significant, exacerbating the difficulties related to elevated skin temperatures of the heating element.
To achieve the required fluid temperature with a heating element of limited thermal capacity, certain prior art systems recirculate the entire flow of contaminated fluid through the entire system until the desired temperature is obtained. Once the desired temperature is reached, valving is shifted to direct flow to the vacuum vessel. The incoming flow of contaminated fluid is then regulated to provide the residence time necessary for sufficient heating. However, such systems are generally relatively inefficient and require operator intervention during startup and transient periods. Moreover, such systems do not effectively avoid the problem of elevated heating element skin temperatures and their effect on the lubricating fluids.
In addition to the drawbacks mentioned above, heretofore known vacuum dehydrating systems often suffer from deficiencies in the structure and operation of their vacuum and fluid evacuation sections. For example, prior art systems of the type described above typically employ an evacuation pump for drawing dehydrated oil from the vacuum vessel. The evacuation pump draws fluid collecting in the bottom of the vessel to circulate the fluids back to the application or reservoir. However, because the evacuation pump draws fluid already subject to a local pressure lower than atmospheric pressure, a certain volume of fluid is generally allowed to collect in the vacuum vessel to provide a reserve of fluid for the evacuation pump. It has been found that larger volumes of collected fluid in the vacuum vessels leads to undesirable foaming of the collected fluid.
In one proposed solution to the problem of dehydrated oil foaming in such systems, a well or sump is provided at the base of the vacuum vessel. The sump is intended to permit the accumulation of a limited amount of decontaminated fluid in the vacuum vessel to maintain the desired feed flow for the evacuation pump and to limit foaming. A system generally of this type is described in U.S. Pat. No. 3,249,438 issued to Topol on May 3, 1966. However, it has been found that such structures are generally insufficient to avoid the collection of significant volumes of fluid in the vacuum vessel, and thus reduce foaming, while adequately supplying the evacuation pump.
A further drawback in heretofore known vacuum dehydration systems resides in the structure and operation of the vacuum section of the systems. In particular, systems of the type described above typically include a vacuum pump which is operated in an open loop manner to draw the highest possible vacuum in the vacuum vessel. Coalescing filters or other devices may be employed in the vacuum vessel to increase the surface area of the fluid, or otherwise to bring emulsified or entrained water to a surface level to facilitate its evaporation. Such devices may also include various mechanical structures for increasing the overall surface area of the fluid stream as it passes through the vacuum vessel. However, other than the flow of fluid through the vacuum vessel, such systems do not provide for circulation or flow of gasses within the vacuum vessel. Similarly, once the desired maximum vacuum pressure is attained, such systems do not vary the vacuum to obtain optimization of evaporation or flash rates.
There is a need, therefore, for an improved system for removing contaminants, particularly entrained and emulsified water, from lubricating and hydraulic fluids. There is currently a particular need for systems of this type which can be implemented on an as needed basis on existing equipment, or which can be made resident with machinery to remove aqueous and gaseous contaminants on a regular basis in cooperation with other filtration systems for the removal of solid phase contaminants.